1. Field of the Invention
The present invention relates to lens barrels and optical apparatuses including the lens barrels.
2. Description of the Related Art
In general, most components included in lens barrels of video cameras and the like are made of resin, from the viewpoints of productivity, manufacturing cost, and arbitrariness of the shape.
Components included in such a lens barrel may expand and contract with changes in the ambient temperature. Therefore, the positions of lens units often change. Consequently, the focal point may be displaced from the surface of an image pickup device, causing defocusing with high possibility.
To solve this, there are some cameras in which defocusing due to changes in temperature is corrected by moving movable sections of their lens barrels.
For example, Japanese Patent Laid-Open No. 6-289275 discloses a technique in which the focal point of a camera is corrected to be defined at a position close to the image pickup surface by moving a movable section of a lens barrel by an amount predetermined from actual measurements, calculations, or the like, in accordance with the temperature detected by a temperature sensor included in the camera. In this technique, the amount of correction of the movable section is set in accordance with the detected temperature. Therefore, if the focal point at a particular temperature varies, the focus may not be corrected. In this respect, the focal position, i.e., the positions of the respective lens units, at each particular temperature needs to be uniform.
In Japanese Patent Laid-Open No. 11-305100, an exemplary lens barrel is disclosed in which a zoom-lens-moving section is provided between a front section and a middle section, and a focus-lens-moving section is provided between the middle section and a rear section. In this lens barrel, the zoom-lens-moving section and the focus-lens-moving section are guided by a zoom guide bar and a focus guide bar, respectively, along the optical axis.
Recent video cameras, for example, include zoom lens systems having increased zoom ratios. In general, increasing the zoom ratio of a zoom lens system leads to an increase in the positional sensitivities of a plurality of lens units provided in the lens barrel.
Therefore, particularly in a zoom lens system having a high zoom ratio, positional repeatability of each lens unit with respect to temperature is important in the above-described focus correction.
A camera operable over a network can be remotely controlled and therefore tends to be used in environments with extreme temperatures. Such a situation causes a large variation in the temperature of the lens barrel. To correct the focus of such a camera, positional repeatability of each lens unit with respect to temperature is highly important.
In the lens barrel disclosed in Japanese Patent Laid-Open No. 11-305100, the ends of the zoom guide bar are secured to the front section and the middle section, respectively, in a press-fitted manner, and the ends of the focus guide bar are secured to the rear section and the middle section, respectively, in a press-fitted manner. The material and coefficient of linear expansion of the foregoing barrel sections are different from those of the guide bars. Accordingly, the amounts of expansion and contraction of the barrel sections also differ from those of the guide bars at regions where the barrel sections are secured. If there are any temperature change under such circumstances, sliding friction may occur between the guide bars and the securing regions of the barrel sections, preventing expansion and contraction of the lens barrel. Consequently, in the lens barrel disclosed in Japanese Patent Laid-Open No. 11-305100, positional repeatability of each lens unit with respect to temperature may become nonuniform.
If the amounts of deformation of components included in a lens barrel with respect to temperature are nonuniform, positional repeatability of each lens unit also becomes nonuniform.
That is, when the temperature changes from a certain level to another and subsequently returns to the initial level, the lens units may not be at their initial positions, resulting in nonuniform positional repeatability with respect to temperature.
This may cause defocusing even after the focus is corrected by moving the movable barrel sections by amounts determined in accordance with the detected temperature.